feat: expose --log_file flag to customize the log destination

[PratikDhanave]

What

Exposes the klog log_file flag so users can customize where kubectl-ai writes its log, instead of it always being <tmpdir>/kubectl-ai.log.

Why

Fixes #428. The log destination was hard-set in cmd/main.go:

klogFlags.Set("log_file", filepath.Join(os.TempDir(), "kubectl-ai.log"))

…but the log_file flag was never added to the command, so there was no way to change it. v and alsologtostderr are already surfaced the same way; this just adds log_file alongside them.

Change

rootCmd.PersistentFlags().AddGoFlag(klogFlags.Lookup("log_file"))

• Default is unchanged (<tmpdir>/kubectl-ai.log).
• Users can now set --log_file=/path/to/kubectl-ai.log, or --log_file=/dev/null to disable file logging (as the issue requests).

Testing

go build ./... and go vet ./... pass. kubectl-ai --help now lists:

--log_file string   If non-empty, use this log file ... (default ".../kubectl-ai.log")